The present invention relates generally to the field of plasma arc torches, and more particularly to a system and method for ensuring proper alignment of components within a plasma arc torch.
The operation of conventional plasma arc torches is well understood by those skilled in the art. The basic components of these torches are a body, an electrode mounted within the body, a nozzle defining an orifice for a plasma arc, a source of ionizable gas, and an electrical supply for producing an arc in the gas. Upon start-up, an electrical current is supplied to the electrode (generally a cathode) and a pilot arc is initiated in the ionizable gas typically between the electrode and the nozzle (the nozzle defining an anode). Then, a conductive flow of the ionized gas is generated from the electrode to the work piece, wherein the work piece then becomes the anode, and a plasma arc is thus generated from the electrode to the work piece. The ionizable gas can be non-reactive, such as nitrogen, or reactive, such as oxygen or air.
The precision of a cut made by a plasma arc torch is, in large part, a function of the axial alignment of key components of the torch, particularly the electrode and the nozzle. The most exact and precise cuts are obtained when the electrode insert is aligned coaxial with the centerline of the nozzle orifice. The generated arc is-centered in the nozzle orifice by the plasma gas. Thus, any misalignment between the insert and the nozzle orifice results in an axial cant (“skew”) of the arc with respect to the torch centerline. The resulting arc thus does not cut exactly collinear with the torch centerline and the workpieces may have inaccurate dimensions or non-perpendicular edges.
An inherent drawback of plasma arc torches is that certain of the critical components wear out and must be replaced. Such components are commonly referred to as “consumable” components and include, for example, the electrode, nozzle, and swirl ring. Depending on the design of the torch, other components may also be subjected to wear and require periodic replacement. Unfortunately, the consumable components, particularly the nozzle and electrode, are made of expensive materials and must be machined to within relatively exact tolerances. Replacement of these consumable components represents a significant portion of the overall costs associated with plasma arc torch operations.
Upon-replacement of the consumable products, it is imperative for proper operation of the torch that such components are correctly seated and aligned within the torch. Also, the useful life of the consumable products is directly affected by proper alignment of the components. A misaligned component will not only result in an inaccurate cut as described above, but subjects the component to excessive wear, and will result in frequent replacement of the component.
In this regard, a significant effort has been made in the art towards systems and methods for improving proper alignment of components within a torch. For example, U.S. Pat. No. 6,424,082 and U.S. patent application No. 2002/0135283 A1 describe a system for improving component alignment by defining complimentary contoured surfaces between contacting components. The '082 patent and '283 application allege that systems relying on O-rings for centering components and compensating for machining tolerances are ineffective because of substantial inherent variations in the molded cross-sectional profiles of O-rings.
U.S. Pat. No. 5,841,095 describes a system for axially aligning components of a plasma arc torch by the use of springs disposed in the circumferential space between the components. The premise is that the springs will result in a self-centering of the components. However, such spring-type centering devices suffer from non-uniformity of applied pressure, especially for smaller diameter components. Such non-uniform pressure may actually cause axial and/or angular misalignment.
The present invention relates to an improved system for aligning components, particularly consumable components, in a plasma arc torch resulting in increased life of the components and improved operation of the torch.